Ballistic missiles are intended to be discharged from field pieces of various bores, and to carry destructive loads of explosives to be fired upon impact with their targets. Under various conditions various targets may be encountered, and the missile must fire reliably when it impacts steel, water, sand, plywood or mud.
Difficulty is sometimes encountered when missiles must be fired during rain storms: rain drops have been observed as large as six millimeters in diameter, and such a raindrop possesses a very considerable impact force. It has also been observed, however, that the duration of impact of even the largest raindrop is very short, and that the frequency of raindrop impact is very low.